This invention relates to valves and more particularly to a valve having a valve closure that is remotely operable by pressurized fluid to provide precisely controlled rates of fluid flow, and a nonflow condition.
Valves having flexible, resilient valve closure members that require manual deformation or some form of pressure differential to induce a fluid flow condition are well known.
One known manually deformable valve, as shown in U.S. Pat. No. 3,889,675, includes a bulb-shaped diaphragm with a normally closed slit. Manual depression of the bulb causes the slit to open and permit fluid to pass through the diaphragm. However, it is difficult to precisely control th flow of fluid through the diaphragm because the bulb-shaped diaphragm must be depressed between the fingers an amount that is based upon the operator's judgment.
Other known valves with flexible resilient closure members are automatically maintained in a closed position by imposing fluid pressure on the valve closure at a location that is external to the normal flow of fluid, such as shown in U.S. Pat. No. 4,465,258. Under this arrangement, when fluid flow is desired, pressure on the valve closure is reduced below the level of the fluid flow pressure. However, an unexpected drop in fluid pressure on the valve closure is also likely to cause fluid to flow through the valve when such flow is not desired.
Reductions of pressure in a valve to accomplish fluid flow often require intricate pressure reducing or bypass arrangements such as shown in U.S. Pat. Nos. 4,300,748; 3,936,028 and 2,026,916. Many of these valves do not permit precise control of fluid flow rates and the complexity and cost of such valve structures unduly limits their use.
U.S. Pat. No. 3,371,677 shows a deflectable valve closure having sufficient stiffness to normally stop the flow of fluid. If fluid is not delivered under high pressure, the valve will not open. Thus, high pressures must be imposed on the delivery fluid in order to overcome the valve closure stiffness and obtain fluid flow.
It is thus desirable to provide a valve having a closure arrangement that does not require high delivery pressures to open a valve closure, does not require high external pressures to maintain the valve in a closed condition, and does not require intricate fluid bypass arrangements or pressure reducing operations to cause the valve closure to open.